In recent years, manufacturing of lenses by a method (hereinafter, referred to as a liquid droplet method) different form the conventional polishing method has come to be popular, in which droplet method a molten glass droplet dispensed on a lower die is compressed with the upper die and the lower die. Small-diameter lenses and short-focal-length lenses which were conventionally difficult to manufacture have come to be possible to manufacture by use of the liquid droplet method.
For example, a method for manufacturing a non-polished lens by using a liquid droplet method and a manufacturing apparatus are disclosed in patent document 1.
A manufacturing method of an optical element by using a conventional liquid droplet method will be now explained by taking a meniscus lens having a concave surface and a convex surface as an example in reference to FIGS. 6a-6e. FIGS. 6a-6e are schematic drawings to show a manufacturing method of an optical element by using a conventional liquid droplet method.
In FIG. 6a, molten glass droplet 101 is formed on the tip portion of nozzle 40 of glass melted in a fusing furnace which is not shown in the drawing. In FIG. 6b, molten glass droplet 101 drops (arrow head P) by its own weight and drops on molding surface 31 (a concave surface in this example) of lower die 30 for molding. The timing of dropping is detected by an optical means or an electric means by use of dropping sensor 50.
In FIG. 6c, lower die 30, which has the glass droplet 101 on molding surface 31 thereof, is moved (arrow head Q) to direct lower of upper die 20 having molding surface 21 (which is a convex surface in this example), and in FIG. 6d, upper die 20 is downed (arrow head R) to a molding position to perform a press molding after a predetermined time has been elapsed since the molten glass droplet 101 was dropped. After performing press molding for a predetermined time, in FIG. 6e, upper die 20 is lifted (arrow head S) from the molding position to separate upper die 20 and lower die 30 to complete molding of meniscus lens 10.